Oxygen-Independent Mineralization of Acetaldehyde by a Cyclodextrin-Anchored WO₃ Photocatalyst under Visible Light

Photocatalytic degradation of volatile organic compounds (VOCs) using visible light has been widely investigated, but its practical implementation remains constrained by several limiting factors. Here, we prepared carboxymethyl-β-cyclodextrin (CMCD)-anchored WO₃ that enabled visible-light-driven mineralization of acetaldehyde even under O₂-free conditions. Anchoring CMCD on WO₃ facilitated interfacial charge separation, enhancing the photocatalytic performance. Spectroscopic and electrochemical analyses revealed that loading CMCD on WO₃ induced the formation of a charge-transfer complex via C-O-W bonding and extended the charge carrier lifetime by trapping electrons in CMCD. CMCD/WO₃ sustained ^•OH generation under visible light (λ > 420 nm) and fully mineralized acetaldehyde even in the absence of O₂. It also produced dioxygen from water oxidation in O₂-free conditions, supplying O₂ needed to fully mineralize VOCs to CO₂, and it enabled an unconventional three-electron reduction of O₂ to ^•OH. CMCD/WO₃ exhibited a visible light degradation efficiency comparable to that of Pt-loaded WO₃. In particular, CMCD/WO₃ exhibited a higher carbon mass balance for acetaldehyde degradation than Pt/WO₃, and this value remained nearly unchanged under both oxygen-rich and oxygen-free conditions. CMCD/WO₃ also demonstrated long-term stability across repeated photocatalytic cycles with no decomposition of the CMCD structure. These findings highlight a supramolecular design strategy for developing an unconventional visible-light-active photocatalyst for indoor air purification, especially in enclosed or oxygen-depleted environments where conventional photocatalysts fail to operate.